Set ‘ret’ properly for error case to fix the build warning below.

drivers/clk/clk.c: In function ‘clk_register’:
drivers/clk/clk.c:3374:9: warning: ‘ret’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  int i, ret;
         ^~~

Fixes: a494c5b9 ("clk: Aggregate power operation per clk")
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>